Field of the Invention
The present invention relates to a focal-plane shutter and an optical apparatus.
Background Art
An optical apparatus, for example, a digital camera and a still camera, employs a focal-plane shutter. The focal-plane shutter includes a substrate having an opening and a curtain that opens and closes the opening (see JP-A-2014-186126, for example).
The focal-plane shutter exposes an imaging device to light (performs light exposure on imaging device) on the basis of movement of the curtain. The curtain moves between a closed position where the opening of the substrate is closed and an open position where the opening is open. When the light exposure is continuously performed (in continuous photographing action), the curtain moves from the closed position to the open position, and after a predetermined period elapses in the open position, the curtain starts moving back to the closed position. The curtain having moved from the closed position to the open position is deformed due to inertia of the curtain during the movement in some cases. The deformed curtain is displaced from a default position in the optical axis direction.
Focal-plane shutters in recent years are required to shorten the curtain action interval in continuous photographing action for an increase in the number of frames that can be photographed per unit period (frame rate).
When the curtain action interval is shortened, however, the curtain starts moving to the closed position before the displacement in the optical axis direction due to the deformation is eliminated in the open position. The curtain therefore moves in an unstable state, resulting in variation in the light exposure period in some cases. Focal-plane shutters of related art therefore have room for improvement in stableness of the curtain in continuous photographing action for suppression of variation in light exposure period.